Forty years later, some Chernobyl fallout particles still hold much of the reactor fuel’s original structure

Forty years after the 1986 Chernobyl accident, some of the tiny radioactive “hot particles” still lying in Ukrainian soil have kept much of the reactor fuel’s original crystal structure. The finding comes from physicists and crystallographers at Leibniz University Hannover and the Helmholtz-Zentrum Dresden-Rossendorf (HZDR), who examined six particles from two locations.

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The particles measure roughly 8 to 50 micrometers across and remain highly radioactive. The result is narrow and carefully hedged by its authors, and it does not mean the contamination has become harmless. What it adds is a measured look at how the fuel itself has aged, which bears on how quickly such particles might release the radioactive atoms locked inside them.

Six particles, three families

Tobias Weissenborn, a physicist and doctoral candidate at Leibniz University Hannover, describes three classes of particle in the HZDR release as published by ScienceDaily. The first resembles uranium dioxide fuel chemically and physically. The second is encased in or fused with zirconium, formed when melting fuel combined with the metal cladding that surrounded it. The third formed when the graphite moderator caught fire and burned for ten days, oxidizing the fuel into uranium oxides such as U3O8.

That last group matters most for safety, because uranium oxides of this kind are mechanically fragile and can break into fragments that wind can carry. Interesting Engineering described the same oxidized compounds, including triuranium octoxide, as mechanically unstable and a possible inhalation hazard once airborne. The sorting into three families rests on how each grain was altered during the accident, whether by melting against zirconium, by the long graphite fire, or by neither.

How the team looked inside the grains

The team isolated particles from Ukrainian soil samples and mounted them on tungsten electrodes. Because the samples were highly radioactive, they traveled to Grenoble, France, inside several layers of containment, where measurements used synchrotron X-ray diffraction at the Rossendorf Beamline. The beam was focused to about 100 micrometers across. Christoph Hennig, a crystallographer at HZDR, said each particle was measured from 2,000 different angles so that every reflection was captured, as Interesting Engineering reported after the work drew press attention in early October.

The results are written up in the Journal of Hazardous Materials as “X-ray diffraction phase analysis of single hot particles from Chornobyl,” with Weissenborn and Hennig among the authors listed at its DOI. Co-authors named in the journal reference include Laura Leifermann, Paul Hanemann, Eleanor Lawrence Bright, Florian Meurer, Aaron Lehnert, Kristina Kvashnina and Clemens Walther.

What the preserved structure suggests, and what it does not

The finding is that the nuclear fuel in all six particles retained much of its original crystal structure after about 40 years in the environment. The authors read this as a hint that the particles can hold on to fission products, which could limit how far contaminants spread into soil and water if the behavior turns out to be common. Interesting Engineering added that the phase analysis helped estimate how quickly such particles give up radioactive substances, which is the practical question behind the whole exercise. Ynetnews summarized the result as the particles being more chemically stable than previously believed.

The authors are blunt about the limits. Weissenborn said that every single particle has a different structure, and that the experiment covered only six particles from two different locations. He added that there will always be outliers, more persistent particles, that will release radionuclides at a later point in time. For that reason the team says it cannot make universal statements about health risks across the region.

Nor do the findings point toward easing access. The researchers say the results do not suggest that restrictions on the Chornobyl Exclusion Zone can be lifted soon, and the contamination is not becoming harmless simply because the fuel has held its structure. Ynetnews noted that entry into contaminated areas is still allowed only in protective suits.

The timeline of the coverage and the next experiments

The paper itself predates the recent wave of coverage. SciTechDaily dated its own write-up Oct. 18 and gave the study’s publication as Feb. 18, 2026, while Interesting Engineering ran its story on Oct. 7 and the ScienceDaily copy of the HZDR release is dated Oct. 22. Readers meeting the story in late October are therefore seeing a result that has circulated for weeks, not a new announcement.

Weissenborn and Hennig are running further experiments on highly radioactive transuranic phases in the remaining debris, work that would extend the same diffraction approach to material more hazardous than the six particles studied here. No results from that follow-up have been reported in any of the coverage reviewed, so the six-particle result remains the only measured finding available from this team.

This article was produced with the assistance of AI and reviewed by Morning Overview editors prior to publication.

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